In general, it is known that a polysaccharide (of a hydrophilic nature) appropriately functionalized with molecules of a hydrophobic nature can provide an assembling system with nanohydrogel characteristics if it is exposed in particular conditions to an aqueous environment.
Currently known are various methods for preparing nanohydrogels starting from functionalized polysaccharides.
A first of these methods consists in subjecting the functionalized polysaccharide to sonication. Ultrasonic vibrations are able to induce formation of nanohydrogels of small size. Ultrasounds generate in the polymeric dispersion micro-bubbles that by imploding give rise to the phenomenon of cavitation, which promotes separation of the polymeric chains, thus favouring formation of a dispersion of nanoparticles.
Another method consists in solubilizing the functionalized polysaccharide in an appropriate solvent and adding drop by drop the solution obtained in water. In these conditions, the system precipitates inducing formation of nanoparticles.
Yet another method consists in subjecting to dialysis against water or aqueous solution the functionalized polysaccharide once this has been solubilized in an organic solvent. Slow entry of water through the dialysis tubes causes formation of nanohydrogels of small size by spontaneous self-assembly.
Nanohydrogels are acquiring an increasing importance in the pharmaceutical field thanks to the fact that, if they are rendered sterile and apyrogenic, they can be used as compounds for vehicling drugs and be administered both in humans and in animals via inhalatory or parenteral route (i.v., i.m., s.c.,) or else topically, with the aid of an appropriate device.
Nanohydrogels, in fact, can englobe or adsorb a pharmacologically active principle and function as carrier for its administration.
In order to be used as drug carrier, the nanohydrogel must necessarily be subjected to a sterilization treatment. The sterilization methods used by pharmaceutical industries not are, however, totally satisfactory.
One of the main sterilization methods used is filtration by means of filters with a porosity equal to or less than 0.22 μm following the pharmacopoeia recommendations. Even though filtration is possible as a rule with systems of suitable dimensions, it is in any case frequently problematical on account of clogging of the filters themselves due to the interactions that may arise between the nanoparticles and the materials constituting the filters. Furthermore, it has been found that filtration causes, as a mechanical effect, destructuring of the nanoparticles, for example vesicles such as liposomes, causing the loss of the medicament of the bio-active molecules, which remain trapped on the filter, and/or their leakage into the transport liquids.
Another sterilization method consists in irradiation with gamma rays or with a electron flow. This procedure presents the disadvantage of being such as to alter the structure of the fragile bio-active molecules, cause a degradation of the polymers that constitute the pharmaceutical form, and alter the integrity of the system itself.
Another method used for sterilization envisages the use of gases, such as ethylene oxide; this technique, however, is not easy to implement in the presence of substances that can react with the gas itself. Furthermore, also the intimate contact with the pharmaceutical forms, necessary for achieving sterility, may prove problematical, as likewise removal of the gas prior to packaging of the pharmaceutical form itself.
A necessary characteristic to guarantee a correct and controllable use of nanohydrogels in biomedical and pharmaceutical applications regards the dimensional homogeneity of the nanohydrogels themselves. As is known, a high dimensional dishomogeneity may not enable a correct control of the efficacy of the nanohydrogels as drug carriers.
Furthermore, another requirement for a correct use of nanohydrogels as drug carriers is that of guaranteeing effective englobing or adsorption of the pharmacologically active compound in the nanohydrogels themselves.
Finally, there is required the possibility of being able to lyophillize nanohydrogels either by themselves or with the pharmacologically active compound so that they are more convenient to transport, preserve, and handle. At the moment when the nanohydrogels are to be used, they will then be reconstituted by simple addition of water or of a physiological solution. As may be immediately understandable to a person skilled in the sector, in order to be able to guarantee stability of, the nanohydrogels following upon the lyophilization treatment, it is necessary for them to be also effectively protected by suitable cryoprotectants by appropriate addition thereof to the nanohydrogels themselves.
There is hence felt the need to provide a methodology that will be able to provide in a simple and economically advantageous way an effective sterilization of the nanohydrogels and at the time same will be able to guarantee a high dimensional homogeneity of the nanohydrogels themselves.
Furthermore, there is also felt the need to provide a simple and economically advantageous method that will enable “charging” of the nanohydrogels with a pharmacologically active compound and/or with a cryoprotective compound.
The inventors of the present patent application have unexpectedly found a method for sterilization and charging of nanohydrogels that, at the same time, manages to provide a greater dimensional homogeneity as compared to the starting nanohydrogels.